Processes and Methods for the Calcination of Materials

ABSTRACT

A system for the calcination of powder materials comprising a plurality of vertical reactor tubes in which a falling powder is heated about a heating zone by radiation from the externally heated walls of the reactor tubes, in which the calcination process of the powder may be a reaction which liberates a gas, or induces a phase change; wherein the average velocity of the particles of falling powder during its transit through the reactor tubes is 1.0 m/s or less; the powder material flux for each tube is preferably in the range of 0.5-1 kg m-2 s-1, and wherein the length of the heating zone is in the range of 10 to 35 m.

The present invention relates broadly to the means of calciningmaterials in a continuous process, where the calcination is describedherein is a reaction or a phase change, or both, induced by heating thematerials.

There are many processes that have been developed to calcine materials,which have been developed for processing particular materials withparticular fuels. The disclosures of this invention relate to a means offast calcination, known as flash calcination, that uses indirect heatingto provide the energy for the reaction of a powdered material.

Most of the prior art for calcination uses direct heating of thematerials by a combustion gas, whereas indirect heating transfers heatfrom the walls of the reactor, generally by radiation heat transferthough a steel tube from an external combustor. There are generallythree applications of an indirectly heated process, namely (a) toproduce calcined materials with a higher reactivity than direct heatingbecause the short residence time and control of temperature down thereactor reduces internal sintering; and/or (b) to separate thecombustion process from the reaction process so that the calcinedproduct is not contaminated by combustion impurities; and/or (c) toseparate the gases from combustion process and the reaction processes sothat the reaction can be controlled, for example by control of theoxidation state and/or (d), for processing carbonate materials thatliberate CO₂ as the calcination reaction to produce oxides, and whichenables capture of the process CO₂ gas as a pure gas stream.

With respect to CO₂ capture, there are two sources of emissions fromsuch calcination processes. The first source is CO₂ released fromcombustion of a carbon based fuels, and is called herein, “combustionCO₂”, and the second source is “process CO₂” that arises from thereaction process, generally from carbonate materials. A low emissionscalcination process is directed to the reduction of both combustion andprocess CO₂. In a life cycle analysis, the use of renewable, or lowemissions intensity, electrical power is a means of reducing fuel-sideCO₂ emissions. It is projected that the global efforts to reduceemissions will be such the calcined products may be judged by theiremissions intensity, in tonnes of CO₂ emissions per tonne of productwhich includes both fuel and process CO₂. There is a need to reduce theemissions intensity of products made by calcination processes.

There are many established methods for reducing combustion CO₂emissions. One method of reducing combustion emissions is to use“renewable electric power” produced from wind, solar or other processesto indirectly heat the calciner. The cost of generating renewable poweris being reduced rapidly and may become affordable for commodityproducts. Other methods use low emissions combustion process. One methodis to use fuels that are not carbon based, such as such as hydrogen,derived from either “electrolysis” of water, or from the use of carbonbased fuels that have been processed by “pre-combustion” capture toremove the CO₂. Another method is to process the flue gas fromcombustion of carbon based fuels to remove the CO₂ in a process called“post-combustion” capture using a sorbent such as amines, bicarbonates,metal oxides and hydrotalcites. Another method is to use oxygen, insteadof air for combustion of carbon based fuels, in a process called“oxyfuel combustion” to produce a flue gas with a high fraction of CO₂which is readily captured. It would be evident to a person skilled inthe art that combustion emissions from calcination can be reduced byusing renewable electric power, or electrolysis, or pre-combustioncapture, or post-combustion capture, or oxyfuel combustion, orcombinations of these to reduce combustion emissions. In mostcalcination processes that use combustion gases, the hot flue gas isused to directly transfer energy to the material by direct heating, sothat any process emissions are mixed with the flue gas, and theextraction of any process CO₂ adds to the cost and complexity ofreducing process emissions. On the other hand, indirect heating not onlycaptures process CO₂ as a pure gas steam but also provides flexibilityto reduce emissions because any of the low emissions methods describedabove may be used to provide the heat.

The materials that produce process emissions when calcined are carbonatematerials such limestone CaCO₃, dolomite MgCO₃·CaCO₃, magnesite MgCO₃;mixtures of minerals such as required for raw cement meal for theproduction of Portland Cement in which the carbonate minerals mayinclude impure limestones, such as marls and other mixed metalcarbonates, including siderite, FeCO₃; and synthetic carbonate compoundsproduced for the manufacture of specific oxide materials, including forexample, manganese carbonate MnCO₃ produced as intermediates in theproduction of metals and battery materials; and organic materials whichdecompose to produce CO₂. There is a wide range of materials that areprocessed by calcination for a variety of industrial purposes whichproduce process CO₂.

There is a need to capture either, and preferably both, process CO₂ andcombustion CO₂ emissions to reduce the emissions from calcination ofmaterials to mitigate climate change. For example, the cement industryis looking to reduce its CO₂ emissions from calcination of limestonethrough a number of methods which include using of biomass, waste andrenewable electric power as fuels, and a number of CO₂ capture methodsthat include amine capture, oxyfuel firing, calcium looping, and aprocess described herein as Direct Separation. The most desirablesolution for emissions reduction is a process in which the CO₂ captureis achieved by the lowest cost, in $ per tonne of CO₂ emissions avoided.In many of the proposed capture processes, the cost of CO₂ capture issignificant because new chemical and physical processes are required,such as for the amine and oxyfuel methods. In calcium looping, the highmass flows and energy recovery is a barrier to its use. The common themeof each of these processes is that their introduction adds to complexityand cost. An alternative approach, Direct Separation, offers process CO₂capture at no additional energy penalty or the use of new materials, ashas been described by Sceats et. al. in WO2015/077818 “Process andApparatus for Manufacture of Portland Cement” and references therein. Inthis approach, indirect heating of the calciner is used so that theprocess gas stream from processing carbonate minerals is process CO₂,with small amount of impurities from volatilisation of minorconstituents. The general approach of calcining carbonate materialsusing indirect heating has been described by Sceats et. al. inWO2016/077863 “Process and Apparatus for Manufacture of CalcinedCompounds for the Production of Calcined Products” and referencestherein, in which the indirect heating process is extended to the use ofdifferent materials and multiple reactor segments, including electricalpowered segments.

It is noted that the inventions associated with Direct Separationreactors described in WO2015/077818 and WO2016/077863 and referencestherein are indirectly heated flash calcination processes, in which thetimescale of the calcination process is generally in the range of 10-50seconds. WO2015/077818 and WO2016/077863 and references thereingenerally include a general requirement for the input particle size tobe typically less than about 100 microns so that the degree ofcalcination, defined herein as the fraction of the carbonate that isconverted to oxide in the reactor in this residence time, is sufficientfor the applications of the calcined products. One variable thatcontrols the calcination process in a Direct Separation reactor is thewall temperature distribution, so it is usual to refer to the residencetime and the average of this wall temperature as the key variables ofthe reactor design. In Direct Separation reactors the particlespreferably flow downwards under gravity, and the residence time islinked to the terminal velocities of the Particle Size Distribution(PSD) in which the acceleration of the particle fall under gravity isbalanced by the gas-particle friction, which depends on the direction ofthe gas flow.

With respect to residence time and temperature of the reactor,generally, the degree of calcination of the material is preferably atleast 95%, or most preferably at least 97% or more. However, in the caseof cement meal it may be lower, about 85%, because the subsequentprocess of clinkerisation may require an endothermic load, such as whenrotary kilns are used for clinker production. There is a need for aDirect Separation process in which the residence time and temperature ina reactor segment can be controlled to achieve the desired degree ofcalcination of a material. The inventions of this disclosure aredirected, in part, to increasing the residence time and temperature ofDirect Separation reactors.

With respect to the PSD, it is useful to define the three numbers fromthe measured cumulative volume distribution, namely d₁₀ as the diameterat which 10% of the particles, by volume, are less than d₁₀, d₅₀ inwhich 50% are less than d₅₀, and d₉₀ in which 90% are less than d₉₀.There are many applications of calcined powders of carbonate materialsin which the most preferable d₅₀ size is more than about 100 microns,which has been described in the prior art referenced above.Specifically, products covering the range of about d₁₀ to d₉₀ of 0.1 to300 microns, each product with a specified PSD within this range.

Powder materials with a d₅₀ exceeding 100 microns are more readilyhandled than smaller materials with a lower d₅₀, and the products arecommonly used in specific powder applications. There is a need to extendthe Direct Separation technology to enable the production of suchpowdered materials into this range.

In other applications there is a need for materials in the form ofgranules of a millimetre size range, and preferably granules of mixedmaterials, particularly for applications in mineral processing whereentrainment of such products in a gas stream is undesirable, such asslagging for the production of metals such as iron, aluminium andmagnesium; and for application in cement manufacturing where clinkerformation from the reactions between bound particles in granules occursin subsequent process steps to form clinker; and for applications inrefractory products in which briquettes are made before sintering. Thereis a need to extend the Direct Separation technology to enable theproduction of such granulated materials, including the integration ofDirect Separation technology into the production of granulated products.

It would be understood by a person skilled in the art that the PSD ofcalcined material varies considerably for many applications.Specifically, there is a need to reduce emissions for production of suchproducts, so there is a need to apply Direct Separation reactors toprocess carbonate materials across a broad range of particle sizediameters. Large particles fall more quickly through a Direct Separationreactor than smaller particles, so the residence time of largerparticles is reduced compared to small particles. In some cases, it maybe practical to extend the length of a Direct Separator reactor,described in the prior art referenced above, to achieve this desireddegree of calcination. However, it would generally be preferable to usea more compact Direct Separation reactor. The inventions of thisdisclosure may be directed to a calcination process that can processlarger particles than hitherto disclosed for Direct Separation reactors.

The Direct Separation reactors described in WO2015/077818 andWO2016/077863 are described as single tube reactors, where the inputmaterials are typically the order of 8-10 tonnes per hour. For largemanufacturing processes, such as cement, the scale up of the reactors isdesirable, in the order of about 200 tonnes per hour. There is a need toadapt Direct Separation reactors for such scale up, so that the benefitsof the process can be delivered for volume manufacturing.

While the inventions of this disclosure are primarily directed towardsreduction of CO₂ emissions for calcination of carbonate materials, andlimestone and cement raw meal in particular, the inventions may beapplied to the calcination of other materials in which the reaction maybe a phase change, or the reactions release gases other than CO₂.Examples of such calcination processes include the removal of moisture,and water of hydration through the production of steam, thevolatilisation of sulphur compounds, ammonia and acid gases such as HCl.

The project leading to this application has received funding from theEuropean Union's Horizon 2020 research and innovation programme undergrant agreements No. 654465 and 884170.

BACKGROUND

The inventions described in this disclosure have been primarily derivedfrom observing and understanding the calcination of materials containingcalcium carbonate (CaCO₃) in Direct Separations reactors to produce lime(CaO). Such inventions described herein may be considered to beimprovements of WO2015/077818 and WO2016/077863 and references therein,for processing such materials. Further, inventions disclosed may beapplied to Direct Separation reactors to scale up the process, tofacilitate the integration of Direct Separation reactors into industrialprocesses, and to process other materials in Direct Separation reactorsfor any purpose.

It would be understood be a person skilled in the art that theprocessing of calcium carbonate containing materials, includinglimestone, dolomite and cement meal is that that the freshly calcinedlime particles are “sticky”. Early references to this property comesfrom historical documents from lime burners, and the consequences impacton the design of modern production processes which produces significantamounts of CaO. There is a very large literature on the subject which issummarised below.

Lime stickiness is associated with the formation of agglomerates ofparticles, the formation of deposits on cold surfaces, the stickyproperties of beds of the material, and the challenges of conveying ofthe product. The physical origin of the stickiness is associated withthe high surface energy of the CaO produced in the calcination reactionfronts that move through the particle. Without being limited by theory,the calcination reaction produces CaO grains that are order of 20 nm insize, with a surface area of more than 100 m²/g. These small grains havea high surface energy which is spontaneously reduced through a sinteringprocess at high temperature in which the grains grow to greater than 100nm through a process known as Ostwald ripening, which is initiated bythe formation of necks between adjacent CaO grains, followed bydiffusion of CaO through these necks, so that the smaller grains areabsorbed into larger grains. This grain coarsening process reduces thesurface energy as the grain size increases. From the perspective of thepores between the grains, there is a transfer of porosity from mesoporesof 5-10 nm to macropores of greater than 100 nm. The literaturedescribes such sintering through a range of mechanisms through which thesintering rate increases not only with temperature, but also with CO₂and H₂O partial pressures, because sintering is catalysed by thesegases. The catalysis is such that CaO can migrate quickly over lengthscales of microns. The diffusion of CaO is important for processes suchas ceramics and cement manufacture, for slagging of minerals, and theimpacts on flash calcination as described below.

The origin of the “stickiness” of such lime particles is that the necksalso grow between colliding particles, or particles adhered on asurface, or packed in a bed to reduce the surface energy. The physicalsintering processes of grains within a particle is not differentiablefrom the adhesion of particles that are in physical contact. In theliterature of ceramics, cements and slagging processes, the word“sintering” is applied to processes both within and between particles Inthis invention, a relevant aspect of stickiness is the process of“agglomeration” in which particles adhere during the calcination processto an extent that the processing of the agglomerate through the reactoris significantly different from the individual particles, and furtherthat the process of “cascading agglomeration” occurs in whichagglomerates adhere. Without being limited by theory, it is understoodthat (a) agglomerates form from particle-particle collisions in clustersof particles which are created in Direct Separation reactors to minimisegas particle friction and (b) agglomerates are formed more readily inconditions when there is stronger gas-particle turbulence whichincreases the collision rate between particles in a cluster, and (c) thestrength of the adhesion, and its persistence, are a result of thesintering process, and (d) the impact of the persistence of agglomerateson the calcination process may be significant.

Of relevance to Direct Separation reactors, the prior art on CaOsintering also describes the catalytic sintering of the CaO by CO₂, inwhich the initial stages of sintering occur within 30 seconds attemperatures greater than about 800° C. and CO₂ partial pressures aboveabout 5 kPa. Since this sintering time is comparable to the residencetime of 10-50 seconds typically used in Direct Separation reactors,where the CO₂ partial pressure is the order of 100 kPa and thetemperature is the order of 900° C., it is reasonable to expect that anyCaO produced in such Direct Separation reactors would be sintered togive a surface area lower than about 20 m²/g. This has been confirmed inDirect Separation reactors. Because sintering occurs on the residencetime of particles in the reactor, it would be expected that the effectsof “stickiness” between particles will also be apparent, and may impacton the performance of a Direct Separation reactor in processingmaterials that produce CaO in the presence of CO₂. This disclosurefocusses on inventions that either mitigate adverse effects, or thattake advantage of the effects to produce novel materials.

One object of the present inventions may be to provide one or more meansof optimising the design of Direct Separator tube reactors to controlthe impacts of lime stickiness.

Another object of the present inventions may be to provide a means ofscaling up Direct Separation reactors to larger production capacity.

Another object of the present invention may be to describe the use ofthe present inventions to integrate Direct Separation reactors intoindustrial applications, with specific applications to the production ofPortland Cement, iron, aluminium and magnesium metal.

Another object of the present inventions may be the application of theseinventions to processing other materials where the benefits are in asimplification of the process in terms of operations and complexity, orimproved properties of the materials.

Any discussion of the prior art throughout the specification should inno way be considered as an admission that such prior art is widely knownor forms part of common general knowledge in the field.

SUMMARY

The inventions of this patent are generally associated with improvementsof Direct Separation technology.

-   -   (a) Such inventions include a system for the calcination of        powder materials comprising one or more reactor tubes in which a        falling powder is predominately heated by radiation from the        externally heated walls of the tube, in which the calcination        process of the powder may be a reaction which liberates a gas,        or induces a phase change, or both; the average velocity of the        powder during its transit through the reactor is 1.0 m/s or less        and preferably less than 0.2 m/s; the powder material flux for        each tube is preferably in the range of 0.5-1 kg m⁻² s⁻¹, and        the length of the heating zone is in the range of 10 to 35 m.    -   (b) A means of processing larger particles, above 100 μm using a        counterflow of particles and gas;    -   (c) A means of reducing agglomeration and clustering by reducing        gas particle turbulence by using a co-flow of particles and gas;    -   (d) A means of cooling the calcined particle stream from a        Direct Separation reactor and heating the ambient particle        streams for injecting the particles into a Direct Separation        reactor using a counter-flow tube systems, and for lime using        the preheating system to partially calcine and passivate the        particles to inhibit agglomeration and fouling when the        particles are injected into a Direct Separation reactor;    -   (e) A means of efficiently external heating the reactor walls        using closely integrated combustor furnace segments, flameless        combustors with various fuels and electric power heating, and in        the case of carbon based fuels, using post combustion processes        to capture the CO₂ to minimise energy consumption and CO2        emissions.    -   (f) A means of using segmented tubes to enable (i) the        optimisation of the process energy consumption by switching the        process gas pressure, (ii) to inject hot gases and fuels/air        and (iii) production of products through an optimised sequence        of chemical reactions, such as the production of Ca(OH)₂ from        CaCO₃    -   (g) A means of thermally granulating lime using the adhesion        from CaO in CO₂, including mixing the lime with other minerals        to that the granules may be used industrial processes where        slagging or clinkering is important, such as the production of        iron, aluminium with CaO, and magnesium metals from dolime        MgO·CaO.    -   (h) A means of scaling up the process using a number of tubes

Problems to be Solved

The first problem to be solved is to optimise Direct Separation reactorsfor processing materials that produce particles that comprise CaO, andespecially CaO particles in the presence of CO₂.

The second problem to be solved is to optimise Direct Separationreactors to scale up the process to larger throughputs.

The third problem to be solved is the integration of Direct SeparationReactors into a number of industrial processes.

The fourth problem to be solved is the improvement of Direct Separationreactors for calcination of a wide range of materials.

Means for Solving the Problems

In a first aspect of the present invention, there is described a numberof measures that reduce the formation of CaO-induced agglomerates ofparticles injected into a Direct Separation reactor, and reduce thefouling of the metal surfaces through which the heat is transferred, andreduce the propensity of beds of these particles to resist fluidisationfor transport. There are three solutions described, The first solutionis one in which larger CaO particles may be processed to take advantageof the observation that agglomeration is reduced when larger particlesare calcined. The second solution is one in which agglomeration of CaOparticles is reduced by minimising the collision frequency betweenparticles. The third solution is to reduce the propensity of such CaOparticles to stick during a collision.

In a second aspect of the present invention, there is described a meansof promoting agglomeration of CaO particles produced from a DirectSeparation Reactor that uses the inventions described in the firstaspect to make products that require granules of the material for use insubsequent processes, Such processes include the production of PortlandCement from the calcined cement meal produced in Direct Separationreactors; for the production of magnesium metal using the Pidgeonprocess from dolime MgO·CaO produced in a Direct Separation reactor; andfor the production of low emissions lime granules produced in a DirectSeparation reactors for injection into slagging processes used in theproduction for example, of steel and aluminium to remove impurities suchas silicates.

In a third aspect of the present invention, there is described a numberof measures of integrating a Direct Separation reactor into anindustrial process. These measures include the means of preheating inputpowders using waste heat, injecting the powder into the reactor,providing heat to the reactor walls, extracting the process gas streamfrom the reactor, minimising the loss of solids in the exhaust gas, andmeasures to cool the product. The primary need for this aspect is toprovide the measures which minimise the energy required to process amaterial, which is generally provided at ambient conditions, and delivera powder product and exhaust gas streams at the required conditions witha preferably minimal energy consumption.

In a fourth aspect of the present invention, there is described a numberof measures that enable the scale up of the production capacity of asystem that uses Direct Separation reactors. There is a reasonable limitto the diameter of Direct Separation reactor tubes associated with thepenetration depth of radiation into the mix of particles and gas. Thus ascale up of the production capacity is primarily through an array oftubes. The measures of scale up include a means for distribution ofpreheated solids to a number of tubes, a means for heating the powder inseparate tubes in a furnace from combustors, and aggregating the powderstreams and gas streams from the reactor tubes for subsequentprocessing. The primary need for this aspect is to provide the measureswhich minimise the energy required to process a material, which isgenerally provided at ambient conditions, and deliver a powder productand exhaust gas streams at the required conditions with a preferablyminimal energy consumption, to achieve an economy of scale.

In a fifth aspect of the present invention, specific process steps areproposed that facilitate the integration of Direct Separation reactorsinto manufacturing processes, with a primary application being for theproduction of cement clinker.

In a sixth aspect of the present invention may relate to a system forthe calcination of powder materials comprising a plurality of verticalreactor tubes in which a falling powder is heated about a heating zoneby radiation from the externally heated walls of the reactor tubes, inwhich the calcination process of the powder may be a reaction whichliberates a gas, or induces a phase change; wherein the average velocityof the particles of falling powder during its transit through thereactor tubes is 1.0 m/s or less; the powder material flux for each tubeis preferably in the range of 0.5-1 kg m⁻² s⁻¹, and wherein the lengthof the heating zone is in the range of 10 to 35 m.

Preferably, the powder materials comprise compounds or minerals whichwhen heated, liberates a gas, wherein the gas is at least one selectedfrom the group of: carbon dioxide, steam, an acid gas such as hydrogenchloride, and an alkali gas such as ammonia.

Preferably, the mineral is limestone or dolomite.

Preferably, the compounds include silica and clays, such that the powdermaterial is a raw cement meal for the manufacture of Portland cement.

Preferably, the particle volume distribution of the powder material islimited by 90% less than 250 μm diameter and 10% higher than 0.1 μm.

Preferably, the liberated gas flows upwards in the tube against the flowof the calcining powder and wherein the gas is exhausted at the top ofthe system.

Preferably, the liberated gas, and any gas introduced into the systemflows downwards in the reactor tube with the flow of the calciningpowder and wherein the gas is exhausted at the base of the system.

Preferably, an inner tube is placed in each tube and the powder materialflows downwards in a reaction annulus with the liberated gas; andwherein at the base of the reactor, the gas flow is reversed to flow upthrough the inner tube and the liberated gas and any gas introduced intothe system is exhausted at the top of the system.

Preferably, the powder material entrained in the exhausted gas isseparated and reinjected into the system.

Preferably, the injected powder is preheated in a gas-powder preheatersystem prior to injection into the system.

Preferably, the gas-powder preheater system is one or more refractoryheating tubes in which the cold powder material falls through a hotrising gas and is heated by the rising gas, in which average velocity ofthe powder during its transit through a preheater tube is 0.5 m/s orless.

Preferably, the exhausted powder from the base of the system is cooledin a gas-powder cooling system.

Preferably, the gas-powder cooling system is one or more refractorycooling tubes in which the hot powder material falls through a coolrising gas, in which average velocity of the powder during its transitthrough a cooling tube is 0.5 m/s or less.

Preferably, an external heating system for externally heating walls ofthe tube is an integrated combustor and furnace system which enables thecontrol of the temperature profile down the heating zone of the system.

Preferably, the external heating system is a flameless combustion systemwhich enables the control of the temperature profile down the heatingzone of the system.

Preferably, the fuel for the external heating system is at least one gasselected from the group of: natural gas, syngas, town gas, producer gas,and hydrogen; and wherein the combustion gas is air, oxygen or mixturesthereof which have been heated from flue gases of the external heatingsystem.

Preferably, CO₂ in the flue gas is extracted using a regenerativepost-combustion CO₂ capture system, which is at least one selected fromthe group of: an amine sorbent system, a bicarbonate sorbent system, anda calcium looping system.

Preferably, the external heating system is an electrically poweredfurnace, where the power is generated from hot gas streams in aproduction plant of which the system is a part, or extracted from thegrid, and configured to enable the control of the temperature profiledown the heating zone of the system.

Preferably, the external heating system is a combination of any one ofthe external heating systems of Claims 14, 15 and 18, which may beapplied to different segments of each tube or different tubes, and theoperation of the system can use a variable combination of such externalheating systems while maintaining continuous production of calcinedmaterials.

Preferably, the powder material is injected into the reactor tubes at anumber of depths.

Preferably, each tube is segmented into a plurality of segments mountedin series, in which the gases liberated or introduced in each segment iswithdrawn from that segment using a gas-block between segments.

Preferably, the partial pressure of the gas liberated during thecalcination in a higher segment may be reduced in the segment below sothat the reaction proceeds further by the partial pressure drop so as toachieve a new equilibrium at the lower partial pressure, including adrop in the wall temperature of the lower segment so that any thermalenergy stored in the partially calcined powder from the higher segmentis used for calcination.

Preferably, the wall temperature of each segment increases sequentiallyin each segment from the upper segment so that the gas liberated fromeach segment can be a specific gas of a desired purity, and other gasesmay be added to each segment to promote catalysis of the reaction stepand/or sintering of the materials during the reaction step.

Preferably, the system makes sintered MgO for refractory blocks frommagnesite.

Preferably, the system produces Ca(OH)₂ or Mg(OH)₂ from limestone ormagnesite.

Preferably, the system controls the oxidation state of batteryprecursors.

Preferably, each tube is segmented into a number of segments, in whichthe gases liberated or introduced in each segment is withdrawn from thatsegment using a gas-block between segments and a hot gas stream isintroduced into a segment to boost the thermal energy of the gas andparticles in that segment to augment the thermal energy provided byexternal heating.

Preferably, the gas stream contains a combustible fuel and oxygen or airfor combustion to induce combustion in that segment to boost the thermalenergy of the gas and particles in that segment to augment the thermalenergy provided by external heating in that or other segments.

Preferably, the temperature rise from combustion is sufficient to induceparticle-particle or intraparticle reactions typical of roasting orclinkering reactions which subsequently occur in the powder bed formedat the base of the segment wherein the energy released from exothermicreactions can sustain or increase the temperature of the powder bed sothat the induced reactions are sufficiently complete during theresidence time in the powder bed.

Preferably, the preheating temperature of the gas-powder preheatersystem is in the range of 650 to 800° C., and the partial pressure ofthe gas liberated during calcination is below 15 kPa so that the powdermaterial is partly calcined and then sintered such that the surfaceenergy of the particle is reduced sufficiently so that the propensity ofthe particles to subsequently bind and agglomerate is reduced.

Preferably, the material is limestone where the calcined material, ormixtures of calcined material with other minerals, is introduced intopost-processing system to produce granules of the materials, in whichthe granules are formed by agitating the powders and wherein the gasenvironment contains carbon dioxide, in which the temperature of thegranulator system is in the range of 650 to 800° C. that recombinationof the lime with CO₂ is suppressed.

Preferably, the material is to be first calcined in a first segmentusing steel reactor walls to provide heat to the system and the gasliberated or introduced in each segments is withdrawn from that segmentusing a gas-block between this first segment and the lower segment, sothat a second gas stream of a different gas may be injected into thesecond segment and heat transfer through the reactor wall in the secondsegment is controlled so that the calcined powder from the first segmentreacts with the gas to produce a new material compound.

Preferably, the powder material is limestone, CaCO₃, or dolomiteCaCO₃·MgCO₃, in which the calcined product from the first segment islime CaO or dolime CaO·MgO and wherein the exhausted gas is CO₂, and thegas injected into the second segment is steam H₂O and the temperature iscontrolled by the removal of heat through the wall so that hydrated limeis exhausted from the second segment and the diameter of the tubes inthe system are selected such that the residence time allow the heattransfers and the reaction kinetics to be balanced with a minimalsegment length.

Preferably, the hydrated lime or dolime product has a high reactivitywith CO₂ in ambient air to reform CaCO₃ or MgCO₃·CaCO₃, and where thisproduct is reintroduced into the system so as to remove CO₂ from ambientair in a cyclic system, and wherein when the product is used withrenewable fuels and with combustion CO₂ capture, the system produces acarbon negative emissions product.

Preferably, the reactor tubes are vibrated to remove the build-up ofsolid materials adhered to the walls of the system.

Preferably, the heat from the external heating system to each tube isseparated by a refractory wall such that the plant can operate with anynumber of tubes in an efficient manner through the use of refractorymaterials and energy distribution, including gas and radiation, whichcontrols the exposure of any tube to radiation and convection transferof heat so that the temperature profile are controlled within desirablelimits linked to thermal stresses of the metal tube, and energyconsumption by the system.

Preferably, the preheater segment and/or the cooling segment requiresthe distribution of preheated materials from a central preheater to eachtube which is accomplished by at least one of the group of: an L-valve,an assembly of L-valves designed to provide a controlled distribution ofpowder to each tube, an aggregator system of the hot calcined materialsfrom each tube to a central cooling system, and a central subsequentprocessing system such a kiln where the aggregation is accomplished by asystem of gas-slides where the flows of hot calcined powder arecontrolled to provide a continuous flow of materials.

The solutions to the problems may be drawn from a number of theseaspects.

Further forms of the invention will be apparent from the description anddrawings.

BRIEF DESCRIPTION OF THE FIGURES

Embodiments of the invention will be better understood and readilyapparent to one of ordinary skill in the art from the following writtendescription, by way of example only, and in conjunction with thedrawings, in which:

FIG. 1 is a schematic of an example embodiment wherein the residencetime of preferably large particles in a Direct Separation reactor isenhanced by the counter-flow of the process gas stream to reduce theterminal velocities of the particles. Any undesirable effects from CaOinducing particle-particle binding is reduced by the use of sufficientlylarge particles, which have a low propensity to bind.

FIG. 2 is a schematic of an example embodiment for preferably calciningsmall particles where CaO induced particle-particle binding is limitedby the use of a co-flow of particles and the process gas withgas-particle separation occurring in the base of the reactor by aseparator.

FIG. 3 is a schematic of an example embodiment for preferably calciningsmall particles where CaO induced particle-particle binding is limitedby the use of a Direct Separation reactor design that has a centraltube, where the reaction occurs in the low turbulence co-flow ofparticles and gas down the annulus, and the process gas is exhaustedthrough the centre tube, wherein the gas-particle separation occurs atthe base of the reactor by a reversal of the direction of the gas flow.

FIG. 4 is a schematic of an example embodiment for preferably calciningsmall particles where CaO induced particle-particle binding is furtherreduced from that of the designs described in FIG. 1-3 by in whichpartial pre-calcining, controlled agglomeration and sintering is carriedout prior to injection in the reactor.

FIG. 5 which the powder is injected into the reactor zone at severaldepths to mitigate the effects of agglomeration.

FIG. 6 is a schematic embodiment in which the powder exhaust from any ofthe Direct Separator reactor configurations of FIGS. 1-5 is and agitatedto produce a ball of agglomerates of a desired size, in which thecompression strength of the granules is sufficiently strong forparticular applications.

FIG. 7 is a schematic of an example embodiment in which the partiallycalcined powder from a first reactor segment is injected into a secondreactor segment where the gas stream is injected into the second reactorsegment.

FIG. 8 is a schematic of an example embodiment for particularapplication to the production of cement clinker in which the powderexhaust from the Direct Separation reactor is processed in several stepsto produce cement clinker by flash heating of the powder by directheating of the falling powder to provide sufficient energy that theclinkerisation reactions may commence, and the heated at the base of thereactor falls into a moving bed where the exothermic clinkerisationreactions proceed and which further heat the bed so that clinker israpidly formed in that bed. Other industrial applications for thisgeneral process are described.

FIG. 9 is a schematic example of an example embodiment of a counterflowDirect Separation reactor of FIG. 1 for the processing of limestone inwhich the furnace heat is provided by a flameless regenerativecombustion process; the fuel is Syngas produced from biomass; the CO₂ isextracted from the flue gas; the heat from the product solid and processgas streams is used to preheat the powder input using a counterflow heatexchangers. The intent of this embodiment is to illustrate that thissystem can provide a high thermal efficiency with complete process andcombustion CO₂ capture to give an overall carbon negative emissionsproduct.

FIG. 10 is a schematic of an example embodiment of a module of DirectSeparation reactors in which the reactors of any of FIGS. 1-10 arehoused in a single furnace where the radiation and convective couplingof the tubes is controlled by the use of refractory elements within thefurnace, and the majority of the product preheating and cooling iscarried out using the ancillaries described in FIG. 10 for each tube.

FIG. 11 is a schematic of an example embodiment of a module of DirectSeparation reactors in which the reactors of any of FIGS. 1-11 arehoused in a single furnace where the radiation and convective couplingof the tubes is controlled by the use of refractory elements within thefurnace, and the preheating and post processing of the materials iscarried out using module-scale systems necessitating the distribution ofpreheated powder and calcined powder from such module scale systems toand from the tubes.

DESCRIPTION OF THE INVENTION

Preferred embodiments of the invention will now be described byreference to the accompanying drawings and non-limiting examples.

With reference to the first aspect associated with the reduction of CaOagglomerates, the principles have been developed based on a knowledge ofgas-particle hydrodynamics considered below. In all the embodimentsdescribed below the particles flow down the Direct Separation reactoragainst gravity.

To inhibit the formation of agglomerates, the preferred approach is toincrease the mean particle size for a fixed mass flow rate. The basisrationale is that the number density of particles is greatly reduced, sothe particle-particle collision rate is reduced, and in addition, themomentum from particle-particle collisions is sufficiently large thatthe necks of CaO produced during a collision are insufficiently strongand fracture, so the colliding particles rebound instead of sticking.The prior art for Direct Separation reactors generally considersparticles to be the order of 20 μm, and generally less than 100 μm. Anobject of the inventions disclosed herein is to increase the particlesize to about 250 μm. There are three factors that lower the degree ofcalcination that can be achieved for such large particles. Firstly, theresidence time of the particles is reduced because the particles reach ahigher terminal velocity from their higher mass; secondly the adsorptionof radiation by the particles from the hot wall is reduced because themean surface area is reduced; and thirdly, for many materials which havea low porosity, the time it takes for the reaction front to move fromthe surface to the centre of the particles is longer for largerparticles. One solution is simply to increase the length of the reactorso that the residence time increases. However, in many cases thissolution is not practical. Another solution is to increase the walltemperature of the reactor so the heat transfer rates are faster.However, in many cases the steel of the reactor tube is unable towithstand the higher temperature because of the loss of strength of thesteel and acceleration of corrosion mechanisms. New steels may alleviatesuch effect.

Another solution is illustrated in FIG. 1 , where the residence time canbe reduced by using a counterflow configuration in which the particleterminal velocity is reduced by the gas particle friction against therising gas produced from the reaction. In FIG. 1 , a Direct SeparatorReactor with counterflow is described in which a powder feed 101 isinjected into the reactor system by a rotary valve 102 into an injectortube 103 into the reactor tube 104. The falling powder 105, in a plume,is heated towards the reaction temperature by the hot rising process gasstream 106 rising from the reaction zone 107 by gas-particle heattransfer by virtue of the counterflow. The cooled gas is separated fromany entrained powder by a system comprising a system of separator plates108 and a tangential gas ejector tube 109 to give a cooled process gasstream 110. Any powder in this gas stream is extracted by acyclone/filter system (not shown) and reinjected into the reactor. Theheated powder 111 in the reactor falls slowly against the rising gas andenters the reaction zone 107 where it is heated by radiation from thereactor walls where the heat is generated within a furnace 112 whichheats the steel walls 113 and the heat flows to the gas and particles inthe reactor to induce the desired reaction. The length of the heatingzone is sufficient for the reaction to be completed to the desireddegree. The falling hot calcined powder is collected in the reactor cone114 and forms a hot calcined powder bed 115 which is extracted from thereactor by an exhaust valve 116, which may be a system of flap valves togive a calcined powder stream 117. An advantage of this configuration isthat the heat transfer between the falling particles and the rising hotgas is to heat the particles so that the process is not as reliant onexternal heat exchangers to achieve a high thermal efficiency. It isnoted that in many cases that this approach may not appear effective,because particles of such a mass and size are, in principle, readilyejected from the reactor. However, it is known that the slipstream oflarge particles shows a strong gas eddy behind the falling particle,such that there is a tendency of the particles to form clusters whichminimise the gas particle friction so the cluster flows down the tubeagainst the rising gas. In addition, the re-injection of any entrainedparticles into the reactor is such that the mass of particlesaccumulated in the reactor grows to a point where the particles havesufficient mass density that they organise as clusters to break throughthe upflowing gas. At high mass flow rates, the clustering of theparticles is sufficient that the momentum of the clusters leads to amore laminar flow regime by the fast exchange of particles betweenclusters, so that large-scale turbulence may by suppressed, with theadded advantage that the growth of fouling may be suppressed by suchmomentum as the particles flow against the wall to minimise thegas-particle friction. Further, it is noted that no process gas iscreated if no particles are injected into the heating zone of thereactor. Thus, a condition is always formed in which the particles mustflow down the reactor. One effect of the configuration of FIG. 1 is thatpulsations may occur of the mass flow through the reactor, and any sucheffects may be controlled by the reactor and the cyclone/filtersettings. Another advantage of the configuration of FIG. 1 is that theparticle flow into the base of the reactor is not impacted by a gasflow, and because the larger particles in the bed of the reactor are notsubject to significant agglomeration as small particles, the conveyingand transport of the particles from the reactor is not inhibited. It hasbeen found that a small injection of preferably hot steam, or air, atthe base may be used to control any such agglomeration. The steam or airin the gas CO₂ gas stream is condensed or removed during the compressionprocess using standard processes. It is preferable that these gases areless than 10% of the process gas stream, and most preferably less than5%. Such a hot gas may also regulate the residence time of the powder,and if the gas is preferably steam or air, the reduction of the partialpressure may increase the degree of calcination by a reduction of theequilibrium pressure of the calcination reaction. Further, in the caseof calcination of carbonates, the displacement of CO₂ at the reactorbase can reduce residual particle agglomeration in the bed at the baseof the reactor to facilitate fluidisation and reduce effects likerat-holing.

Another advantage of the configuration of FIG. 1 is that the lowstrength of particle-particle bonds between larger particles is suchthat fouling of the tube surface to limit heat transfer is less thanobserved for small particles. Experiments show that the vertical surfaceof the tube is self-cleaning for both small and large particles, andsections of coated surface sloughs off at high temperatures suggestingthat the strength of the interparticle bonds are sufficiently weak tosupport a thick coating, so the fouling is typically less than 1 mmthick. It is found that the thickness of the coating, as measured by thetemperature drop between the inner steel wall and the exposed coatingsurface decreases as the particle flux increases, as may be expectedfrom the increased shear forces created by the higher momentum of thesolids which dislodges the coating. This is a characteristic of the allthe configurations disclosed below. The thickness however, depends onthe embodiments described herein, and the learning is that suppressionof agglomeration is correlated with a lower coating thickness.

It is noted that this configuration of FIG. 1 may be generally appliedto the calcination of materials in which there is little tendency forthe large particles to agglomerate. The longer residence time and thelow loss of powder due to clustering in counterflow is generally abenefit. In applications where the process is a pyroprocessing phasechange, the injection of gas at the base may increase the residencetime, and that gas may be chosen as one which catalyses the phasechange. An example is the processing of α-spodumene to β-spodumene toextract lithium, and the catalyst is steam.

There are many cases in which it is not possible to increase theparticle size of the powder input, so that approach of the embodiment ofFIG. 1 is not possible. It has been observed that when small particlesare injected into a Direct Separation reactor, that there may bemultiple effects that are encountered when CaO is formed by calcination.These include an increase in the fouling of the hot steel reactorsurfaces that creates a resistance to the heat transfer of radiation forthe walls into the bulk of the reactor, an increased resistance of thepowder collected in the base of the reactor to flow, and the formationof large agglomerates that form in the reactor that fall through thereactor sufficiently fast that the degree of calcination is reduced. Asdescribed above, all these effects can be attributed to the stickinessof the lime produced during calcination. The formation of large granulesof lime, up to several mm is size may be formed, in which case theprocess is called “cascading agglomeration” because large agglomeratesof this size are formed by agglomeration of agglomerates. In otherconditions the size of the agglomerates is smaller, say about 100-150μm. While such conditions may be found and the calcination of suchagglomerates may achieve a desired degree of calcination, the onset ofcascading agglomeration from limited agglomeration is difficult tomanage, and this is undesirable for quality control.

The principle for reducing agglomeration is to minimise the turbulenceof the gas particle flows on all length scales, because high turbulencemaximises the particle-particle and particle-wall collision frequencyand, the suppression of turbulence limits the formation of agglomerates.The embodiments of FIGS. 2 and 3 provide examples in which agglomerationmay be controlled by minimising the turbulence. FIG. 2 described aco-flow system in which the process gas stream is exhausted at the baseof the reactor and FIG. 3 describes a system in which the process gasstream is exhausted through a central tube whereby the gas stream isexhausted at the top of the reactor.

In FIG. 2 , a Direct Separator Reactor with co-flow is described inwhich a powder feed 201 is injected into the by a Rotary Valve 202 intoan Injector Tube 203 into the Reactor Tube 204. The falling powder 205,in a plume, is heated towards the reaction temperature by radiation fromthe steel reactor walls 206 which heats the gas and particles, where theheat is generated within an external furnace 207 which heats the steelwalls. The heated powder 208 falls deeper into the reactor into reactionzone 209 where the radiation heat from the walls is absorbed and inducesthe desired reaction. As the reaction proceeds, the hot process gas 210accelerates the particles through the reactor by virtue of the co-flow.The length of the heating zone is sufficient for the reaction to becompleted to the desired degree. The calcined powder 211 and the hotprocess gas 212 are exhausted from the base of the reactor. These gasand particle streams are separated by the reactor cone 213, the gasejector tube 214 and the powder bed 215 acting as an inertial separatorwhich forces the hot process gas steam 216 to be ejected from thereactor and the powder to be deposited in the powder bed. The hot powderstream 217 is exhausted from the reactor by the exhaust valve 218, whichmay be a system of flap valves. Any powder in this gas stream isextracted by a cyclone/filter system (not shown) and reinjected into thereactor.

In FIG. 3 , a Direct Separator Reactor with co-flow is described inwhich a powder feed 301 is injected by a Rotary Valve 302 into anInjector Tube 303 into the reactor tube 304. The falling powder 305, ina plume, is defected by a defected cap 306 into a reaction annulus,formed by a hanging central tube 307 (the suspension of which is notspecified). The falling powder 308 is heated towards the reactiontemperature in the annulus by radiation from the steel walls 309 heatedby the furnace 310. The heated powder 311 falls deeper into the reactorinto reaction zone 312 where the radiation heat from the walls isabsorbed and induces the desired reaction. As the reaction proceeds, thehot process gas 313 accelerates the particles through the reactor byvirtue of the co-flow. The length of the heating zone is sufficient forthe reaction to be completed to the desired degree in the annulus. Thegas and particle streams are separated by the reactor cone 314, and thepowder bed 315 which forces the hot process gas steam 316 into thecentral tube 307, to be ejected from the reactor through the gas ejectortube 317, and the powder is deposited in the calcined powder bed. Thehot powder stream 317 is exhausted from the reactor by the exhaust valve319, which may be a system of flap valves. Any powder in the gas stream317 is extracted by a cyclone/filter system (not shown) and reinjectedinto the reactor.

The essential difference between FIGS. 1 and 3 is that in FIG. 3 thereis a physical barrier to separate the gas and powder streams. It isnoted that there is a tendency for the powder to preferably flow downnear the outer wall of the reactor in FIG. 1 because it is know fromfundamental principles that the gas particle friction is lowest in thatregion.

One relative advantage of the central tube in FIG. 3 is that thevelocity of the rising gas stream maty be high so that the size of thecyclone at the top of the reactor for separation of the fines is smallerthan an inertial separator; and particles are re-injected into thereactor at the top, whereas the efficiency of the large inertialseparator at the base of the reactor is low, and a cyclone/filter isrequired to separate the fines. Another advantage is that the centraltube can absorb radiation from the from the hot external tube, and thistube can re-radiate the energy to the gas-particle stream so the netheat transfer rate can be optimised. Another advantage is that the hotCO₂ stream exhausted from the top of the reactor can be used topartially preheat the input powder stream in say, a cyclone. This aspectis considered separately below with respect to integration optimisation.Another advantage of the central tube is that the extraction efficiencyat the base can be enhanced by adding swirling elements near the end ofthe tube in the annulus and swirling elements of blades near theentrance of the inner tube in a way that both these elements create anadditive flow pattern to the gas above the cone of the reactor basewhich enhances the separation efficiency of the particles and gas in theregion below the central tube. Nevertheless, the gas particle separationat the base is sufficiently effective without either of these options.It is noted that the central tube of FIG. 3 may be perforated, orconstructed from hanging segments, and that within that tube, blades maybe used to swirl the gas so that any entrained powder may be extractedfrom that gas flow by an in-line ejector into the annulus. Theembodiment of FIG. 3 may be preferred because it provides such optionsThere are additional options for mitigating agglomeration and itsassociated impacts. The sintering of the particle reaction surfaces wasconsidered above. One such surface is the external surface of theparticle, and a reaction front is developed initially at this surface,so that this surface begins to sinter at the commencement of calcinationso the propensity to bind particles reduces from that point. In manyconfigurations of Direct Separation reactors, the particles arepreheated before injection into those reactors. FIG. 4 shows an exampleembodiment in which the preheating process can be used to passivate, toa degree, the external particle surfaces by partly calcining andsintering the surface.

It would be understood by a person skilled in the art that thetemperature at which calcination commences can be lowered by loweringthe partial pressure of CO₂, and that the preheating of the powder canbe managed using low-CO₂ gas streams such surface calcination commencesin the preheater to a controlled degree. In FIG. 4 , a pre-heatingsegment for preheating/calcining/sintering system is described. Powderfeed 401 at a temperature below the calcination temperature, asdescribed below, is injected by a rotary valve 402 into an injector tube403 which delivers the particles into the refractory lined heat exchangereactor tube 404 to give an injected falling powder 405, in a plume. Thehot steam/air stream 406 has a temperature sufficiently high, asdescribed below, to preheat the powder, to induce calcination of thesolids to limited degree, and to sinter the calcined particles isinjected into the base of the system with a tangential gas injector tube407 and flows upwards as a swirling gas flow 408. There is an exchangeof heat between the rising gas and powder streams as they move incounterflow, and the system injection conditions are designed to reducelarge scale turbulence which can optimise the heat transfer between theparticles and the gas. The rising gas stream is exhausted through asystem of separator plates 409 and a tangential gas ejector tube 410 togas exhaust 411. Any powder in the cooled gas stream 411 is extracted bya cyclone/filter system (not shown) and reinjected into the reactor. Thefalling heated powder 412 forms a bed 413 in the cone 414. The hotpowder exhaust 415 is exhausted from the system using an exhaust valve416, which may be a system of flap valves. The temperature of the inputsand mass flow rates are such that the degree of calcination of the CaOmaterial in preferably less than 10%, and most preferably less than 5%,and the residence time of the powder in the bed is such that thesintering of the powder in the powder stream 415 is such that thestickiness of the surface layer is such that the particles have areduced tendency to agglomerate when injected into the calciners.

The sintering of the CaO on the surface can be accelerated bytransferring the preheated powder in a portion of the hot CO₂ gas sothat the catalytic sintering described above can be accelerated so thatthe powder is passivated to degree by the holding time of the powder ina feed hopper. In an alternative option is that a small amount of steammay be injected into the bed of the preheated pre-calcined particles topassivate the powder. Without being limited by theory, the sintering ofCaO occurs more quickly in steam than CO₂, and the reaction of steam toform Ca(OH)₂ can be inhibited by maintaining the temperature of thematerial above about 580° C. In most cases, the preheating of the powderis limited by the energy available to about 720° C., so this conditionmay be met. The second feature of this embodiment is the injection ofthe preheated powder into the reactor at a number of points down thereactor. The intent of this approach is to lower the particle density atpoints higher in the reactor so that the agglomeration rate at thosepoints in reduced. Such an embodiment is illustrated in FIG. 5 , inwhich, a Direct Separator reactor with counterflow, similar to that ofFIG. 1 , is described in which a powder feed 501 is injected into the bya rotary valve 502 into an injector tube system 503 into the reactortube 504. The reactor tube system in this embodiment comprises threeconcentric tubes compared to FIG. 1 which has one tube, The tubes havedifferent lengths so that the powder is released into the reactor atdifferent heights. The falling powder 505 from each such tube is heatedtowards the reaction temperature by the hot rising process gas stream506 rising from the reaction zone 507 by gas-particle heat transfer byvirtue of the counterflow. The cooled gas is separated from anyentrained powder by a system comprising a system of separator plates 508and a tangential gas ejector tube 509 to give a cooled process gasstream 510. Any powder in this gas stream is extracted by acyclone/filter system (not shown) and reinjected into the reactor. Theheated powder steams 511 from each tube in the reactor accumulates andfall slowly against the rising gas and enters the reaction zone 507where it is heated by radiation from the reactor walls where the heat isgenerated within a furnace 512 which heats the steel walls 513 and theheat flows to the gas and particles in the reactor to induce the desiredreaction. The length of the heating zone is sufficient for the reactionto be completed to the desired degree. The falling hot calcined powderis collected in the reactor cone 514 and forms a hot calcined powder bed515 which is extracted from the reactor by an exhaust valve 516, whichmay be a system of flap valves to give the calcined powder stream 517.

It is noted that the degree of inhibition of agglomeration achieved bysintering may be limited because the CO₂ or H₂O binds to the surface andfacilitates fast surface migration of CaO at a sufficiently hightemperature. This property may be used to manufacture new materials andapplications for low emissions lime produced by Direct Separationreactors. It is noted that granules of limestone, or lime, are currentlyused in wide range of high temperature pyrolytic metallurgical processas a slagging agent, to remove silica and other impurities. Groundlimestone was often used in these process, but the endothermic load fromcalcination of the limestone to CaO is very high, so that lime iscommonly used. In these processes, fine lime powder is not used becausethe lime particles are entrained by the gas streams in suchpyroprocesses, and lime granules of mm size are preferably used. Theability of Direct Separation reactors to make low emissions lime is ofinterest, but the particle size is limited, as explained above. However,from experimental observations, the fresh lime produced from thesereactors may my readily balled into granules which may be heat treatedto produce a granule with the strength required to be used in suchprocesses. The example embodiment of FIG. 6 shows how such a process maybe produce such granules. FIG. 6 is a granulator system in which apowder 601 and CO₂ containing gas 602 is injected into a heated rotarydrum 603, which is heated by a heating element 604 to produce granules605 at a sufficiently high temperature that the CaO is not recarbonated.A property of these granules is that they are inherently porous. Thus asecond application is the use of such granules to capture gases such asSO_(x) and CO₂ in a fixed bed, and the performance of these granules forsuch processes is enhanced by virtue of the fact that in the interior ofthe particle the reactivity of the CaO is higher than the lime made byconventional processes using high emissions lime. In another example,granules of CaO materials are strong, porous and permeable, and may beused absorb H₂O, SO_(x), CO₂, Cl₂, H₂S and other gases and metal vapourswithout cracking. In a further example, the high surface reactivity ofthe CaO may be used to produce granules of a mixture of powders. Forexample, the granule may be comprised of silicate containing mineralssuch as iron ore for the production of steel, or kaolin for theproduction of alumina, where the CaO in the granule may be used in asubsequent process, under appropriate conditions to form calciumsilicates by a slagging process. For magnesium metal, the CaO containingmaterial may be dolime, mixed with a reductant such as ferrosilicon,which when heated form magnesium vapour and a calcium-iron silicateslag. In all such cases the granules provide the close contact where themigration of CaO facilitates slag formation.

The prior art described above recognises that Direct Separation reactorsmay be segmented into different zones. One example is a post-processingsegment in which the powder from a Direct Separation reactor isprocessed to complete the reaction process. It is understood that theresidence time to complete a calcination reaction may very long becausethe reaction rate slows down as the reaction nears completion. There maybe requirements for a very high degree of calcination for differentproducts and applications. FIG. 7 describe embodiments that may be usedto achieve a target for calcination in lieu of extending the length ofthe reactor. In FIG. 7 , a general two segment Direct Separation reactoris described in which the first reactor segment is similar to that ofFIG. 1 and the second reactor segment below the first is used tocomplete the calcination reaction by a number of different designsdescribed below, and the two segments are separated by a gas block. Thegas block operates by having a high mass flow of powder which, by virtueof the gas-particle friction substantially inhibits the flow of gas fromthe second segment to the first segment. The powder feed 701 is injectedinto the by a rotary valve 702 into an injection tube 703 into thereactor tube 704. The falling powder 705, in a plume, is heated towardsthe reaction temperature by the hot rising process gas stream 706 risingfrom the first reaction zone segment 707 by gas-particle heat transferby virtue of the counterflow. The cooled gas is separated from anyentrained powder by a system comprising a system of separator plates 708and a tangential gas ejector tube 709 to give a cooled process gasstream 710. Any powder in this gas stream is extracted by acyclone/filter system (not shown) and reinjected into the reactor. Theheated powder 711 in the reactor falls slowly against the rising gas andenters the reaction zone where it is heated by radiation from thereactor walls where the heat is generated within a furnace 712 whichheats the steel walls 713 and the heat flows to the gas and particles inthe reactor to induce the desired reaction. The length of the heatingzone is sufficient for the reaction to be completed to an intermediatedesired degree, and the calcined intermediate powder 714 falls into thecone 715 where the powder is concentrated and flows into the gas block716 to fall into the second reactor segment 717. A gas stream 718, witha composition depending on the materials and the mode of operation ofthis embodiment is injected into this reactor segment where it interactswith the powder and is exhausted from the reactor segment as stream 719.The efficiency of the gas block is set by the gas pressure drop acrossthe two reactor segments. The temperature of the reactor segment wallsmay be controlled by the externally heated furnace or cooling segment720 if required by the application. The desired reaction goes tocompletion in this segment to give a calcined power 721, which iscollected in the reactor cone 722 and forms a hot calcined powder bed723 which is extracted from the reactor by an exhaust valve 724, whichmay be a system of flap valves to give a calcined powder stream 725.

In the case of the production of CaO, where the reaction is incomplete,the temperature of the partially calcined powder 714 will be slightlyabove about 895° C. In one use of the embodiment of FIG. 7 CO₂ partialpressure in the first segment is about 103 kPa and is dropped to about10 kPa by the injection of air or steam 718 so that the reactionrecommences when the powder is transferred into the second segment. Thecalcination may go to completion by consuming the heat in the powder, orby applying additional heat as required from the furnace 720. The sameconsiderations apply to the production of MgO. If steam is used thetemperature must be maintained above the relevant hydrationtemperatures.

In another example of the system embodiment of FIG. 7 , the secondsegment is used to sinter the intermediate material 714. In a specificexample, the intermediate is MgO produced from the calcination of MgCO₃as the feed 701, and the gas 718 is steam which in used to catalyse theMgO to give a desirable surface area of the MgO for industrialapplications. Without the steam, the specific surface area may be graterthan about 250-350 m²/g and with steam is can be reduced to less thanabout 10 m²/g.

In another example of the system embodiment of FIG. 7 , the gas 718 maybe a mixture of air, or oxygen, and a combustible material, generally agas such as syngas, which reacts by flameless combustion to generate theheat for the reaction. This mode of operation is facilitated by the hightemperature of the powder feed 714 which is preferably above theautoignition temperature of the combustible material.

It is noted that the second segment may be directly integrated into thefirst stage of the reactor by injecting the air and fuel into the baseof a single segment reactor, in which case the concentration profile ofthe process gas increases as the gas rises in the reactor by thecalcination reaction induced by the partial pressure drop, moderated bythe interdiffusion of the gases.

In another example embodiment of FIG. 7 , the gas 718 injected into thesecond segment have a component which reacts with the calcinedintermediate powder 714 produced in the first segment. In this approach,the first segment is preferably operated to achieve a sufficiently highdegree of calcination so that the reaction between the gas and thepowder in the second segment may produce the desired calcined product725. In addition, the mode of operation of the furnace/cooler 720 is setto established the required reaction conditions, for example providingheat for endothermic reactions or removing heat for exothermicreactions. A specific example is the case in which the calcinedintermediate 714 is CaO from a precursor 701 of limestone, the injectedgas 718 is steam, the furnace/cooling system 720 operates in a coolingmode such that the product 725 is hydrated lime, Ca(OH)₂. The heatrecovered in 720 may be used in the overall process flow to reduce theenergy demand required for the overall process. The same considerationsapply to the production of Mg(OH)₂ from MgO.

A general example for the production of battery and catalyst materialsis one in which the desired reaction is either a reduction or oxidationprocess of the intermediate 718 produced from a precursor 710, and whichis accomplished by using an appropriate reducing or oxidation gas 718and setting the temperature to induce the desired reaction for thedesired product 725.

It would be appreciated by a person skilled in the art that theprinciples described by the example embodiment of the multisegmentsegment FIG. 7 may be applied to any calcination reaction, or pair ofreactions, or sintering reactions, where the gas has a compositionappropriate for the desired process.

The process of Portland cement production occurs in several stages. Theprior art described for Direct Separation reactors describes a processin which the initial stages of the process, namely the calcination ofthe cement raw meal is carried out in a Direct Separation reactor andthe performance of that stage may be improved by the inventionsdescribed in this disclosure. The second stage is carried out in arotary kiln where the calcined meal is injected into the kiln which isheated by a flame to about 1450° C. where the clinkerisation reactionsthat form belite and alite as the dominant cementitious materials areactivated. It is noted that the thermal efficiency of a cement plant istypically about 60% or less because the heat losses from a rotary kilnare high, and the exothermic energy of the clinkerisation reactions isnot used to advantage. The embodiment of FIG. 8 is directed toimprovement of this process. This embodiment describes how the injectionof a combustion gas and air/oxygen may be used to raise the temperatureof the powder exhausted from a Direct Separation reactor by a homogenouscombustion reaction. The application of the embodiment of FIG. 8describes a process within a refractory lined segment in which thecounterflow of the rising reacting air and fuel is used to heat thepowder to a temperature of about 1260° C. or more. In FIG. 8 , aspecific two segment Direct Separation reactor is described for theproduction of clinker from preheated cement meal where an approach istaken to form clinker in a Direct Separation reactor segment. In thisapproach the option of using flap valves to separate the gas steams isused. The preheated cement meal 801, at about 720° C., is injected usinga rotary valve 802 into an injection tube 803 for feeding into thereactor tube 804. The falling preheated powder 805, in a plume, isheated towards the reaction temperature by the hot rising CO₂ processgas stream 806 rising from the first reaction zone segment 807 bygas-particle heat transfer by virtue of the counterflow. The cooled gasis separated from any entrained powder by a system comprising a systemof separator plates 808 and a tangential gas ejector tube 809 to give acooled process gas stream 810, at about the same temperature as 801. Anypowder in this gas stream is extracted by a cyclone/filter system (notshown) and reinjected into the reactor. The heated powder 811 in thereactor falls slowly against the rising gas and enters the reaction zonewhere it is heated by radiation from the reactor walls where the heat isgenerated within a furnace 812 which heats the steel walls 813 and theheat flows to the gas and particles in the reactor to induce the desiredreaction. The length of the heating zone is sufficient for the reactionto be completed to an intermediate desired degree and the calcinedcement meal powder 814 falls into the cone 815 where the powder isconcentrated and is fed by a flap valve 816 to fall into the secondreactor segment 817. A fuel stream 818 and an oxygen/air stream 819 isinjected into this reactor segment where it undergoes flamelesscombustion and heats the powder 820. The reactor wall 821 is refractorytube. The combustion process heats the powder 822 to a temperature ofabout 1260° C. which marks the onset of the clinkerisation reactions toform belite. The hot particles fall into the vertical kiln segment 823,in a slowly moving bed where the particle-particle contacts allows theseexothermic clinker reactions to proceed, and the heat released drivesthe temperature to about 1450° C. or more, where alite is formed whenthe residence time of the bed of about 30 minutes or less. The exothermgoes to completion in this segment to give a clinker granules. Theexhaust valves 824 empties the hot clinker granules 825 from thevertical kiln, where they are cooled by air using conventional gratingcoolers (not shown). It would be appreciated by a person skilled in theart that FIG. 8 describes an energy efficient process because theexothermic reactions heat the meal, unlike the conventional kiln processwhich has a high heat loss.

A high energy efficiency of an industrial process is an importantfactor. With regard to the reactor, the thermal energy efficiency for agiven degree of calcination is not impacted by virtue of using a DirectSeparation reactor. Any heat losses are associated with the heat lossesthrough the refractory skin surrounding the furnace and combustorsegments of the reactor. In this embodiment, the inventions are extendedto a consideration of the combustor-furnace configuration. Importantfactors for heat transfer are the temperature and the convective heatexchange to the steel reactor walls and the refractory of the furnace,so that the radiation heat transfer through the steel walls isoptimised. Generally, this is optimised by the known arts of using highgas velocities and a swirl of the gas. The Direct Separation reactorsmay be operated by using a separate combustor box and piping the hotflue gas into the furnace that surrounds the reactor tube in a way thatgives these desirable properties, and the hot flue gas exhaust may beused to preheat the air for the combustion. However, the ducting anddistribution of high temperature gases is not desirable. In FIG. 9 , andexample embodiment for the processing of limestone illustrates adifferent approach. The selected fuel is Syngas from Biomass and apostcombustion CO₂ capture system is used to illustrate a carbonnegative product when the CO₂ stream is sequestered (not shown). Ingeneral terms, it is desirable to have a close integration of thecombustor, the furnace and air recuperation processes to reduce the airvolume required. The embodiment of FIG. 9 shows that array ofrecuperative flameless systems is may be applied to reduce the flue gasvolume flow In such a system, the combustor and furnace are integrated,and the temperature of gas is uniform, from the absence of a flame, andthe high velocity of the mixed gases. The thermal efficiency of aregenerative flameless combustor is very high, and the absence of aflame minimises the production of NOx. The use of a distribution of suchsystems allows the control of the temperature along the tube, whichallows optimisation of the calcination process in the tube. In theembodiment of FIG. 9 a system, using a Direct Separation reactor isdescribed which processes a limestone feed 901, ground to about a d₅₀ of125 μm is processed to lime 902. The reactor system has three segments—afirst powder preheater segment 903, a second powder preheater segment904, a Direct Separation reactor segment 905 and a powder cooler segment906. In the first powder preheater segment, the limestone process hotCO₂ stream 907 is injected into the base of a counterflow heat exchangerefractory lined tube of the first powder preheat segment 903 into whichthe limestone powder 901, at ambient temperature is injected to give acooled CO₂ gas stream 910 and a partially heated limestone 911 which isformed into a bed. The partially heated limestone 911 from the bed isinjected into the top of a heat exchange refractory lined tube of thesecond powder preheat segment 904 where is heated by a hot air stream912 from the powder cooler segment 906 described below and the preheatedlimestone 913 is formed into a bed. If required, the temperature of thisair stream may be boosted by a duct heater (not shown) for thetemperature of the preheated limestone is at or near the onset ofcalcination of limestone at about 930° C. The cooled air stream 914 isexhausted, but may be used (not shown) to supply low grade heat to thePost Combustion CO₂ capture system 915 for the flue gas described below.The preheated limestone 913 is injected into a Direct Separation reactorsegment 905, here shown as a counterflow system of FIG. 1 to give a purestream of processed CO₂ 907 which is ejected at about the temperature ofthe preheated limestone, and a hot lime powder 916. The DirectSeparation reactor is heated by combustion of a hot Syngas stream 917formed from biomass 918 and air 919 in a Gasifier 920. In the Gasifier,the Syngas the ash 921 is separated. The tars formed in the gasificationprocess may be reinjected into the hot Syngas steam. The steel tube 922of the Direct Separation reactor segment 903 is heated by the combustionof the hot Syngas by a number of regenerative flame combustion systems,one of which 922 injects air 923 which is preheated by the hot exhaustflue gas from the combustor in the heat exchanger 924 so that the fluegas steam 925 is cooled to give a high thermal efficiency combustionprocess. The CO₂ from that gas stream is injected into the PostCombustion CO₂ capture system 915 where the CO₂ 926 is extracted andmixed with the direct separation gas steam 910 to give the CO₂ steam 927for compression and liquefaction (not shown).

The CO₂ emissions from fossil fuel combustion gases is a significantcontribution to the CO₂ emissions intensity of a calcined product. Forlime and cement, with typical solid fossil fuels such a coal, thecombustion emissions is about 35% of the total emissions. One approachto reduce combustion emissions is to use a biofuel and, in combinationwith a Direct Separation reactor. Biofuels are generally solid fuels,called biomass, which may be gasified to Syngas using know art, andwhich may be used in the configuration of FIG. 9 . An integratedgasification process gasification process is carried out using the knowart of heating the biomass, in steam/air, to release the combustiblevolatiles and to separate and combust the ash, including the fly ash,with its residual carbon, to provide the heat for volatilisation in anindirectly heated process. The hot volatiles are combusted in aflameless combustor using preheated air. In this process, the gas maycomprise syngas as well as tar precursors, because they are combusted.That is, the costly processes of removing the tar precursors is notrequired because the gas is maintained above the tar condensationprocess, so the fuel is not only preheated, but has a higher LHV forcombustion. The removal of the fly ash from the gas stream is performedto minimise the formation of glassy deposits of silica on the steelwalls of the furnace. The Post Combustion capture process in FIG. 9 mayuse either amines, bicarbonates or hydrotalcites.

The embodiments described above, and exemplified by the examples ofFIGS. 1-9 are associated with reactor based on a single tube. The scaleup of the processing by expanding the diameter of reactor is limited bythe absorption of heat from the hot walls by the particles and theprocess gas, and the mass flow is limited by the capacity of the wallsto transfer heat and the engagement of the particles in the process gaswhich impacts on the residence time of the particle in the reactor tube.Generally, the mas flow through the reactor with a diameter of about 2 mis in the range of 5-10 tonnes/hr. The height of the reactor depends onthe kinetics of the process and the heat transfer rate from the walls,and is typically 10-30 m. It follows that the scale up of the process isto increase the number of tubes. However, there are innovationsassociated with the design of an array of reactor tubes, and these aredescribed herein. FIG. 10 is an example embodiment of a scaled up systemin which the tubes, shown as four in the embodiment, are assembled intoa furnace in which the amount of refractory between the tubes isminimised so that any tube can be shut down with minimal impact onadjacent tubes. The temperature of the non-operating tube issufficiently low that there is no risk of distortion of that tube, andthe set points of the operating tube may be adjusted to maintain thedegree of calcination of the product and other process variables. Thiscondition may be achieved in the module so that any tube may be inoperation, and the process flow in each tube may be varied with atolerable, known thermal coupling between the tubes. In the embodimentof FIG. 10 , the refractory may be constructed from stacked cast blocksthat provide to the integration into the input fuel gas and flue gasdistribution systems of the module, and flameless combustors are shown.The cast blocks are designed so as to minimise the refractory mass, andthe cost of construction and replacement. In this embodiment, each tubehas its own preheating and post-processing systems to minimise thetransport of hot gases and powders. The embodiment of FIG. 10 is aschematic of a reactor module of 102 of four Direct Separation Reactors1,2,3,4 which are integrated into a refractory 103. This system is basedon a concept that conveying cold powders and cold gas steam are a knownart with the costs and challenges being reduced by lowest temperature ofthese process flows. The embodiment shows in input of ambient powder104, a source of gaseous fuel 105 and ambient air 106. The directseparation reactor are based on the embodiment of FIG. 1 and thecombustors of FIG. 9 . Thus the input powder is conveyed by cold powderconveyors 107 from the hopper 104 into each Reactor through separatelines to the respective Stage 1 Preheaters PH1-1,2,3,4 which cool theprocess CO₂ 108 from each Direct Separator reactor segment DS-1,2,3,4,and are directed to the central CO₂ clean/up compressor system 109. Theflue gas 110 from the reactor combustors, after recuperation with theincoming air streams, are directed to the post-combustion capture plant111 to give a combustion CO₂ stream 112, which then compressed, and aflue gas. In the case of the production of cement meal, the hot thepowder streams from each reactor may be transferred to a rotary kiln bythe air slides described in the embodiment of FIG. 11 below.

A number of modules as described in FIG. 10 may be used for furtherscale up. An advantage of this approach is that any tube which may berendered inoperable may be replaced while the other tubes can continueto operate, and also that such tubes may be commissioned and itsoperations can be optimised at each stage of preheating, calcination andcooling to deliver a calcined product to meet specifications.

There are scale up gains that may be made in which the ancillaries thatare used to preheat and postprocess the powders and gas steams may bescaled into single modules. While such an approach requires distributionof hot gases and powders, there are a number of approaches that may beused to achieve the benefit of such scaling. Such a system is shown inFIG. 11 in which a module of four tubes has a single preheater stack sothat the preheated powder is uniformly distributed to the tubes using a1:4 L-valve distribution system with controls to allow any number oftubes to be fed; the calcined powder streams are collected using a 4:1heated air slide system which have similar controls; and the hot CO₂streams are combined to give a single CO₂ steam for postprocessing andcompression. Such a heat recuperation system is known to scale from theuse of suspension cyclones in cement plants. In this embodiment the heatin the combined CO₂ stream is used to preheat the powder in the firststage of a cyclone stack. For the production of cement, the hot airslide would deliver the hot calcined meal to a single rotary kiln (notshown). The embodiment of FIG. 11 is a schematic of a system that uses areactor module of 111 of four Direct Separation Reactors 1,2,3,4 whichare integrated into a refractory 113. This system is based on a conceptthat conveying hot powders and hot gas steams are a known arts, with thehigher costs and challenges for these elements being offset by the useof large scale preheaters and coolers rather than, in the embodiment ofFIG. 10 where each reactor required an separate systems. The embodimentshows in input of preheated powder 114, a source of gaseous fuel 115 andambient air 116. The direct separation reactor are based on theembodiment of FIG. 1 and the combustors of FIG. 9 . In the case of hotpowders, a means of controlling the flow rate into each tube is throughthe use an L-valve fluidised bed 117 fluidised by hot air 118, and theheat each loss in each conveyor tube is minimised by a refractory pipe.The conveyor system for the preheated powder for each tube, ifpneumatic, is steeply inclined to avoid saltation. Each reactor DS1,DS2, DS3, DS4 generates a hot process CO₂ stream which is aggregated toa hot CO₂ stream 119, and a hot flue gas stream 120 which are conveyedto a central preheater for the powder through refractory coated pipes(not shown). The calcined powder streams Cal1, Cal2, Cal3 and Cal4 fromeach tube are conveyed by a system of tubes, and one example, theconveying is achieved by a refractory enclosed, inclined hot air slide121. The aggregated hot calcined materials 122 are generally injectedinto to a powder cooling system (not shown) or, in the case of cementproduction, a rotary kiln system.

Although the invention has been described with reference to specificexamples, it will be appreciated by those skilled in the art that theinvention may be embodied in many other forms, in keeping with the broadprinciples and the spirit of the invention described herein.

The present invention and the described preferred embodimentsspecifically include at least one feature that is industrial applicable.

1. A system for calcination of a powder material comprising a pluralityof vertical reactor tubes in which a falling powder is heated within aheating zone by radiation from one or more externally heated walls ofthe reactor tubes, in which the calcination process of the powder is areaction which liberates a gas, or induces a phase change; wherein anaverage velocity of the particles of the falling powder during itstransit through the reactor tubes is 1.0 m/s or less; a flux associatedwith the powder material for each tube is in a range of 0.5-1 kg m-2s-1, and wherein a length of the heating zone is in a range of 10 to 35m.
 2. The system according to claim 1, wherein the powder materialcomprises one or more compounds or minerals which when heated, liberatesa gas, wherein the gas is at least one selected from the group of:carbon dioxide, steam, an acid gas such as hydrogen chloride, and analkali gas such as ammonia.
 3. The system according to claim 2, in whichthe mineral is limestone or dolomite.
 4. The system according to claim3, in which the compounds include silica and clays, such that the powdermaterial is a raw cement meal for the manufacture of Portland cement. 5.The system according to claim 1, in which a particle volume distributionof the powder material is limited by 90% less than 250 μm diameter and10% higher than 0.1 μm.
 6. The system according to claim 1, in which theliberated gas flows upwards in the tube against the flow of thecalcining powder material and wherein the gas is exhausted at a top ofthe system.
 7. The system according to claim 1, in which the liberatedgas, and any gas introduced into the system flows downwards in thereactor tube with the flow of the calcining powder and wherein the gasis exhausted at a base of the system.
 8. The system according to claim1, in which an inner tube is placed in each tube and the powder materialflows downwards in a reaction annulus with the liberated gas; andwherein at a base of the reactor, the gas flow is reversed to flow upthrough the inner tube and the liberated gas and any gas introduced intothe system is exhausted at a top of the system.
 9. The system accordingto claim 1, in which the powder material entrained in any exhausted gasliberated by the calcification process is separated and reinjected intothe system.
 10. The system according to claim 9, in which the injectedpowder is preheated in a gas-powder preheater system prior to injectioninto the system.
 11. The system according to claim 10, in which thegas-powder preheater system is one or more refractory heating tubes inwhich the cold powder material falls through a hot rising gas and isheated by the hot rising gas, in which average velocity of the powderduring its transit through a preheater tube is 0.5 m/s or less.
 12. Thesystem according to claim 9, in which an exhausted powder from a base ofthe system is cooled in a gas-powder cooling system.
 13. The system ofclaim 12, in which the gas-powder cooling system is one or morerefractory cooling tubes in which any hot powder material falls througha cool rising gas, in which average velocity of the powder materialduring its transit through a cooling tube is 0.5 m/s or less.
 14. Thesystem according to claim 1, in which an external heating system forexternally heating the walls of the tube is an integrated combustor andfurnace system which enables control of a temperature profile down theheating zone of the system.
 15. The system according to claim 14, inwhich the external heating system is a flameless combustion system whichenables the control of the temperature profile down the heating zone ofthe system.
 16. The system according to claim 14, in which a fuel forthe external heating system is at least one gas selected from the groupof: natural gas, syngas, town gas, producer gas, and hydrogen; andwherein a gas used for combusting the fuel is air, oxygen or mixturesthereof which have been heated from flue gases of the external heatingsystem.
 17. The system according to claim 16, in which CO2 in the fluegases is extracted using a regenerative post-combustion CO2 capturesystem, which includes at least one substance selected from the groupof: an amine sorbent system, a bicarbonate sorbent system, and a calciumlooping system.
 18. The system according to claim 14, in which theexternal heating system is an electrically powered furnace, where theelectrical power is generated from hot gas streams in a production plantof which the system is a part, or extracted from an electricity grid,and configured to enable the control of a temperature profile down theheating zone of the system.
 19. The system according to claim 14, inwhich the external heating system includes a plurality of heatingsubsystems, with the heating subsystems being associated with differentsegments of each tube or different tubes, and the operation of thesystem can use a variable combination of such external heatingsubsystems while maintaining a continuous production of calcinedmaterials.
 20. The system according to claim 1, in which the powdermaterial is injected into the reactor tubes at a number of depths. 21.The system according to claim 1, in which each tube is segmented into aplurality of segments mounted in series, in which any gases liberated orintroduced in each segment are withdrawn from that segment using agas-block between segments.
 22. The system according to claim 21, inwhich a partial pressure of the gas liberated during the calcination ina higher segment may be reduced in a lower segment located below thehigher segment, so that the reaction proceeds further by a partialpressure drop to a lower partial pressure so as to achieve a newequilibrium at the lower partial pressure, including a drop in a walltemperature of the lower segment so that any thermal energy stored inthe partially calcined powder from the higher segment is used forcalcination.
 23. The system according to claim 21 wherein a walltemperature of each segment increases sequentially in each segment froman upper segment so that any gas liberated from each segment can be aspecific gas of a desired purity, and other gases may be added to eachsegment to promote catalysis of the reaction step or sintering of thematerials during the reaction step.
 24. The system according to claim23, wherein the system makes sintered MgO for refractory blocks frommagnesite.
 25. The system according to claim 23, wherein the systemproduces Ca(OH)2 or Mg(OH)2 from limestone or magnesite.
 26. The systemaccording to claim 23, wherein the system controls an oxidation state ofbattery precursors.
 27. The system according to claim 1, in which eachtube is segmented into a number of segments, in which any gasesliberated or introduced in each segment are withdrawn from that segmentusing a gas-block between segments, and a hot gas stream is introducedinto a segment to boost a thermal energy of the gas and particles inthat segment to augment a thermal energy provided by external heating.28. The system according to claim 27, in which the gas stream in asegment contains a combustible fuel and oxygen or air for combustion toinduce combustion in that segment to boost the thermal energy of the gasand particles in that segment to augment the thermal energy provided byexternal heating in that or other segments.
 29. The system according toclaim 27, in which the temperature rise from combustion is sufficient toinduce particle-particle or intraparticle reactions typical of roastingor clinkering reactions which subsequently occur in a powder bed formedat a base of a segment wherein the energy released from exothermicreactions can sustain or increase the temperature of the powder bed sothat the induced reactions are sufficiently complete during theresidence time in the powder bed.
 30. The system according to claim 10,in which a preheating temperature of the gas-powder preheater system isin a range of 650 to 800° C., and a partial pressure of the gasliberated during calcination is below 15 kPa, so that the powdermaterial is partly calcined and then sintered such that a surface energyof an associated particle is reduced sufficiently so that a propensityof the particles to subsequently bind and agglomerate is reduced. 31.The system according to claim 1, in which the material is limestonewhere the calcined material, or mixtures of calcined material with otherminerals, is introduced into a post-processing system to producegranules of the materials, in which the granules are formed by agitatingthe powders and wherein the gas environment contains carbon dioxide, inwhich a temperature of a granulator system included in thepost-processing system is in a range of 650 to 800° C. thatrecombination of lime associated with the limestone with CO2 issuppressed.
 32. The system according to claim 1, in which the materialis to be first calcined in a first segment using steel reactor walls toprovide heat to the system and the gas liberated or introduced in eachsegments is withdrawn from that segment using a gas-block between thisfirst segment and a lower segment, so that a second gas stream of adifferent gas may be injected into the lower segment and heat transferthrough a reactor wall in the second lower segment is controlled so thatthe calcined powder from the first segment reacts with the gas toproduce a new material compound.
 33. The system according to claim 32,in which the powder material is limestone, CaCO3, or dolomiteCaCO3·MgCO3, in which the calcined product from the first segment islime CaO or dolime CaO·MgO and wherein the exhausted gas is CO2, and thegas injected into the second segment is steam H2O and the temperature iscontrolled by the removal of heat through the wall so that hydrated limeis exhausted from the second segment and a diameter of the tubes in thesystem is selected such that a residence time allows associated heattransfers and reaction kinetics to be balanced with a substantiallyreduced segment length.
 34. The system according to claim 33, in whichthe hydrated lime or dolime product has a high reactivity with CO2 inambient air to reform CaCO3 or MgCO3·CaCO3, and where this product isreintroduced into the system so as to remove CO2 from ambient air in acyclic system, and wherein when the product is used with renewable fuelsand with combustion CO2 capture, the system produces a carbon negativeemissions product.
 35. The system according to claim 1, in which thereactor tubes are vibrated to remove a build-up of solid materialsadhered to the walls of the system.
 36. The system according to claim 1,in which heat from the external heating system to each tube is separatedby a refractory wall such that a plant including the system can operatewith any number of tubes in an efficient manner through the use ofrefractory materials and energy distribution, including gas andradiation, which controls an exposure of any tube to radiation andconvection transfer of heat so that a temperature profile is controlledwithin desirable limits linked to thermal stresses of the metal tube,and energy consumption by the system.
 37. The system according to claim36, in which a preheater segment and/or one or more cooling segmentrequires a distribution of preheated materials from a central preheaterto each tube which is accomplished by at least one of the group of: anL-valve, an assembly of L-valves designed to provide a controlleddistribution of powder to each tube, an aggregator system of the hotcalcined materials from each tube to a central cooling system, and acentral subsequent processing system such a kiln where the aggregationis accomplished by a system of gas-slides where the flows of hotcalcined powder are controlled to provide a continuous flow ofmaterials.